With the realization of high recording density of a magnetic recording medium, high performance of magnetic heads is now required. In order to realize high recording density, the line recording density and track density of a magnetic recording medium must be improved, which means a magnetic head should assure high frequency recording and less recording blur. Here, a "recording blur" means the phenomenon of the recording magnetic field spreading in the track width direction at the time of data writing enough to influence adjacent tracks.
Particular attention is now focused on magneto-resistive ("MR") heads that can be used for a small size disk apparatus while assuring high output which does not depend on the velocity of the magnetic recording medium. This MR head satisfies the requirement for high recording density. As a magnetic head having a MR head, a specific magnetic head called a composite type head is well known. This composite type head is formed by stacking in the laminating direction. It has a reproducing head of multilayer structure to read magnetic information from a magnetic recording medium and a recording head of multilayer structure to write information to the magnetic recording medium.
There is a member at the boundary of the reproducing head and the recording head. In particular, a magnetic shield layer (upper magnetic shield layer) in the side of the reproducing head is also used as the lower magnetic pole in the side of the recording head among a pair of magnetic poles of the recording head. Therefore, the surface (ABS or floating surface) of the lower magnetic pole, which is part of the recording head opposite to the magnetic recording medium, is formed wider than the width of the recording tracks of the magnetic recording medium. As a result, in the writing operation, the recording magnetic field is generated from the lower magnetic pole, which spreads widely in the track direction of the recording medium. However, it becomes difficult to narrow the track width and reduce the track pitch, both being requirements for high recording density. Both upper and lower magnetic poles of the recording head are connected at the center area of an eddy type recording coil, and a recording magnetic field is generated over the Air Bearing Surface ("ABS") between the lower magnetic pole and the upper magnetic pole. In order to improve the recording density, it is required to set the core width of the ABS of the upper magnetic pole to a small size (1 .mu.m or less) to reduce the recording blur. However, there are some barriers for realizing fine width of the core.
As illustrated in FIG. 1, since a recording coil 112 is embedded in an interlayer insulating layer 111 formed between the upper and lower magnetic poles, a large difference of levels exists at the surface of the interlayer insulating layer 111. Therefore, liquid resist 115, coated on the interlayer insulating layer 111, used in the process of forming the upper magnetic pole, flows toward the lower level area. As a result, the resist 115 becomes thin at the higher level area (flat area) but becomes comparatively thick at the lower level area (bottom area).
In the process of forming the upper magnetic pole, resist 115 is first formed at the surface of interlayer insulating layer 111 and is then patterned to the predetermined shape. The upper magnetic pole is formed by plating on the area of the interlayer insulating layer 111 from which the resist 115 is removed. In order to form the upper magnetic pole in the predetermined thickness, the thickness of the resist on the flat area is required to be about 6 .mu.m. However, due to the existence of level (or thickness) differences of the interlayer insulating layer, the thickness of the resist on the bottom area becomes about 10 .mu.m. Here, it is very difficult to realize a target core width of 10 .mu.m or less for the ABS of the upper magnetic pole when the resist is formed in the thickness of 10 .mu.m or more.
In order to solve this problem, the applicant of the present invention has proposed, in Japanese Published Unexamined Patent Application No. HEI 9-109845 (Apr. 25, 1997), a partial trimming technique for the upper magnetic pole using a focused ion beam (FIB). In particular, it has been proposed that the upper magnetic pole be locally trimmed by the FIB method from the ABS surface side in order to narrow the core width during composite type magnetic head manufacturing process.
FIGS. 2(a) and 2(b) show a process of trimming the upper magnetic pole using the focused ion beam method. As shown in FIG. 2(a), the upper magnetic pole 116 covers a part of an eddy type recording coil 112. Moreover, the upper magnetic pole 116 includes a pole 116a which is elongated in the area adjacent to the recording medium.
FIG. 2(b) is a view showing the trimming process using the focused ion beam method for the pole 116a. In the trimming process, the lower magnetic pole located at both side portions and the lower area of the pole 116a (the area in contact with the gap layer of the upper magnetic pole 116) is trimmed by irradiation of the focused ion beam. With this trimming process, the width of the pole 116a of the upper magnetic pole 116 is shaped to the desired size, and a groove (trench) or recess is formed in the upper layer of the lower magnetic pole located at both lower areas of the pole.
As explained above, the width of the pole 116a can be finished in the fine dimension using the focused ion beam method. Spread in the track width direction of the recording magnetic field generated between the upper and lower magnetic poles can be minimized using the upper magnetic pole 116 having the pole of fine width. As a result, the writing of data in higher track density can be realized on the magnetic recording medium.
However, trimming of the upper magnetic pole using the focused ion beam will deteriorate productivity. In the focused ion beam method, the ion beam is focused to predetermined positions in both sides of the pole to set the ion irradiation area in every head element to trim the width of the pole to 1 .mu.m or less. Because a plurality of head elements are formed on a wafer substrate, longer time is required since the process must be repeated for each head element. For example, even if the processing time of one head element is about 10 seconds, it will take over a day (27.7 hours) for processing only a sheet of wafer because there are about 10,000 heads in a 5-inch wafer, which is still comparatively small in size. It is simply not practical to use focused ion beam equipment for actual production.
The applicant of the present invention has proposed to replace the use of the focused ion beam method disclosed in Japanese Published Unexamined Patent Application No. HEI 10-184780 (Jun. 25, 1998) for trimming the upper magnetic pole with the ion milling method.
FIGS. 3(a) and 3(b) illustrate the trimming of the upper magnetic pole using the ion milling method. FIG. 3(a) is a plan view of the upper magnetic pole, and FIG. 3(b) is a cross-sectional view along the line B--B of FIG. 3(a).
First, as illustrated in FIG. 3(a), resist 26 is coated to the area, except for the object area of trimming when the upper magnetic pole 116 is formed. In practice, the pole 116a of the upper magnetic pole and the area, except for the lower magnetic pole 114 located at the lower area of the pole, are covered with resist. The trimming is performed by radiating the side surface of an elongated pole of the upper magnetic pole and the upper layer of the lower magnetic pole with the ion beam as shown in FIG. 3(b) as the substrate is rotated. In the initial stage of trimming, the incident angle of the ion beam to the side surface of the pole is ranged from 10.degree. to 40.degree., and the upper layer of the lower magnetic pole 114 is mainly trimmed. After the upper layer of the lower magnetic pole 114 is trimmed up to the predetermined depth, the trimming is executed to the side surface of the pole 116a at an incident angle of the ion beam .theta. being set to 50.degree. to 80.degree..
Trimming by this ion milling method makes it possible to shape many head elements formed on the wafer at one time, and therefore the trimming time is reduced to a large extent in comparison to the focused ion beam method.
In Japanese Published Unexamined Patent Application No. HEI 10-184780, the ion beam is irradiated under the condition that the substrate is rotated about an axis and is irradiated at an angle with respect to the axis. Therefore, the head elements formed on the wafer receive the ion beam in various directions. During the period of the ion beam irradiating from the pole side of the upper magnetic pole, the trimming is performed effectively. However, while the period of the ion beam irradiating from the flat area side of the upper magnetic pole, the ion beam is shielded by the flat area of the upper magnetic pole in the higher stacking height. Thus, the target area of trimming is not hit by the ion beam, specifically the upper layer area of the lower magnetic pole. A longer time is then required to finish the head element to the predetermined shape even when using the technique disclosed in Japanese Published Unexamined Patent Application No. HEI 10-184780.
Moreover, in trimming by the ion milling method, the ion beam is radiated not only to the side surface of the pole but also to the upper surface thereof. Since the upper surface of the pole is located at a comparatively high position, it is always irradiated with the ion beam without relation to the irradiating direction of ion beam. Therefore, when the trimming time becomes longer, the reduction in height of pole (pole length) is also increased.
Since the pole length influences the intensity of the magnetic field generated by the recording head, the shorter the pole length becomes the weaker the intensity of the magnetic field becomes. In the recording operation to the recording medium, an adequate intensity of magnetic field to be given to the recording medium is two times the reactive magnetic force of the medium. Since the reactive magnetic force of the recent recording medium is about 2500 (Oe), the magnetic field intensity of about 5000 (Oe) is required. To satisfy this requirement, reduction in pole length due to the ion milling method must be minimized.